Recently, for more improvement of a safe performance and a riding comfort or the like of a vehicle, electronic equipments to be in-car equipped are increased. Moreover, for reducing environmental load, not only a fuel economy improvement but also a popularization of start-stop system or the like is progressed.
With increasing such electronic equipments, popularizing the start-stop system, and the like, a necessity to monitor a condition of a battery and detect quickly a fault, a weak battery, or the like, is rapidly required. Corresponding with this, methods of estimating the state of health (SOH) or the state of charge (SOC) of the battery are proposed in a variety.
According to Patent Document 1, by a predetermined model calculation to calculate a battery voltage, using the battery voltage and based on a predetermined formula, the SOC of the battery is to be calculated. Regarding the above mentioned model calculation, a simple battery model with few element parameters is used. Moreover, the calculation result of the battery voltage and the measured battery voltage are fed back, then the above mentioned element parameters are to be corrected.
Furthermore, according to Patent Document 2, using a performance model of the battery with the SOC and the voltage of the battery as state parameters, by estimating the state based on a Kalman filter, the SOC of the battery is to be evaluated.
That is to say, using the above mentioned performance model of the battery, a voltage change for a measured current is predicted, then based on a differential between the predicted voltage and the measured voltage the state parameters are to be corrected. Hence, the SOC as one of the state parameters is obtained as a corrected result value.
[Patent Document 1] Japanese application publication No. 2004-514249
[Patent Document 2] Japanese application publication No. 2002-319438